Snow control vehicles as are used by governmental highway system authorities and the like as well as within private industry typically are provided as conventional dump trucks which are seasonally modified by the addition of snow-ice treatment components. Such components will include a forwardly-mounted plow which is controllable by hydraulic cylinders for up-down and right-left or angular movement. Upon the rearward end of the truck dump bed there usually is mounted sand-salt dispensing components which include a feed auger extending across the back edge of the dump bed. This auger is rotated by a hydraulic motor to effect movement of material from the bed onto a rotating spreader disk or "spinner" which functions to spread the sand-salt material onto the pavement being treated.
Thus, a hydraulic system for such vehicle is called upon to accommodate not only the dump body hoist but also the variable speed auger, the spinner, and plow control system. Because of the seasonal nature of snow-ice control, these latter function-dedicated components find duty only for a relatively minor portion of the operational life of a truck. Consequently, economic practicality dictates that the hydraulic system employed be as simple as possible while still providing adequate control performance. For example, permanently mounted hydraulic pumps preferably are not elaborate and thus remain "on line" or actively engaged by the truck motor during all periods of truck use, elaborate clutching schemes or the like not being practical from a cost standpoint. In view of their practical structuring, very often gear pumps are employed for the instant purpose. This continuous engagement of the hydraulic pump with the truck motor represents a design trade-off, the penalty for which is the expense of added energy consumption by the continuously coupled motor-pump assemblage.
Control features for the hydraulic systems are called upon to vary the rate of sand/salt distribution both with respect to weather conditions and to truck operation. For example, the speed of truck movement should be associated with the rate of material delivery to the pavement. Because variations in human factor aspects of truck operations can be anticipated, it also is desirable to both provide an automatic distribution control feature and a secure distribution parameter selection for management control regulation of rates of salt/sand distribution. In the latter regard, ecological considerations may enter into the allowable amounts of deposition of chemicals such as salt.